A brake disc rotor for use in the braking system of an automobile or other wheeled vehicle comprises a disc having a central aperture, an inner hollow circular hub by means of which the disc is mounted on a rotating vehicle axle or the like to rotate with the wheels of the vehicle, and an outer, thinner circular peripheral plate part having side braking surfaces. The braking surfaces on the outer part are gripped between stationary brake pads, operating in caliper fashion from each side of the disc rotor when the brakes are applied. In order to give satisfactory performance, the disc or disc rotor must be manufactured and finished to fine tolerances. The braking surfaces must be substantially flat and parallel to the mounting surface of the central hub, so that the disc rotor runs true. Otherwise engagement of the brake pads and braking surfaces will be uneven, causing shuddering and ineffective braking. The thickness of the outer portion of the disc rotor is important since the clearance between the rotating disc surfaces and the brake pads when the brakes are not applied is very small, of the order of 1/32". Further the braking surfaces should be smooth and polished, to allow even and gentle application of the brakes when required.